5. Legal bracket string

【 Problem description 】

A legal string of parentheses , A string that contains only parentheses , If the following conditions are met ：

（1）<> () [] {} These four pairs of brackets are legal ;

（2） If r It's a string of legal brackets , be <r> (r) [r] {r} It's also ;

（3） If r,s It's a string of legal brackets , be rs It's also ;

therefore <<>> , [<>{}(())],[({<>})] Is a legal string of parentheses , and )(,[( ]) It's not .

【 Input form 】

Enter a positive integer in the first line t (10 ≤ n ≤ 100), Indicates how many sets of test data .

In the back t That's ok , Each line contains only 8 A string of parentheses .

40% The length of the string of parentheses L 2 ≤ L≤ 20;

30% The length of the string of parentheses L 2 ≤ L≤ 200;

20% The length of the string of parentheses L 2 ≤ L≤ 2000;

10% The length of the string of parentheses L 2 ≤ L≤ 20000;

【 Output form 】

For each group of test data , If the string of parentheses is legal , Output “Yes”（ The output has no quotation marks ） Occupy a line , otherwise , Output “No”（ The output has no quotation marks ） Occupy a line .

【 The sample input 】

6
<<>> 
)(
[<>{}(())]
[({<>})]
[(])
<([{
  

【 Sample output 】

Yes
No
Yes
Yes
No
No

#include <iostream>
#include <stack>
#include <string>

using namespace std;

int main()
{
    int n;
    cin>>n;
    for(int k=0;k<n;k++)
    {
        string a;
        cin>>a;
        stack<char> s;
        int l=a.length();
        bool flag=true;
        for(int i=0;i<l;i++)
        {
            if(a[i]=='}'||a[i]=='>'||a[i]==']'||a[i]==')')
            {
                if(s.empty())
                {
                    flag=0;
                    break;
                }
            }
            if(a[i]=='('||a[i]=='{'||a[i]=='['||a[i]=='<')
                s.push(a[i]);

            else if(a[i]==')')
            {
                if(s.top()=='(')
                    s.pop();
                else
                {
                    flag=0;
                    break;
                }
            }
            else if(a[i]=='}')
            {
                if(s.top()=='{')
                    s.pop();
                else
                {
                    flag=0;
                    break;
                }
            }
            else if(a[i]==']')
            {
                if(s.top()=='[')
                    s.pop();
                else
                {
                    flag=0;
                    break;
                }
            }
            else if(a[i]=='>')
            {
                if(s.top()=='<')
                    s.pop();
                else
                {
                    flag=0;
                    break;
                }
            }
        }
        if(s.empty()&&flag)
            cout<<"Yes"<<endl;
        else
            cout<<"No"<<endl;
    }

    return 0;
}